Feize Li

Biosorption of uranium on Bacillus sp. dwc-2: preliminary investigation on mechanism

In this paper, the biosorption mechanisms of uranium on an aerobic Bacillus sp. dwc-2, isolated from a potential disposal site for (ultra-) low uraniferous radioactive waste in Southwest China, was explored by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, FT-IR spectroscopy, proton induced X-ray emission (PIXE) and enhanced proton backscattering spectrometry (EPBS). The biosorption experiments for uranium were carried out at a low pH (pH 3.0), where the uranium solution speciation is dominated by highly mobile uranyl ions. The bioaccumulation was found to be the potential mechanism involved in uranium biosorption by Bacillus sp. dwc-2, and the bioaccumulated uranium was deposited in the cell interior as needle shaped particles at pH 3.0, as revealed by TEM analysis as well as EDX spectra. FTIR analysis further suggested that the absorbed uranium was bound to amino, phosphate and carboxyl groups of bacterial cells. Additionally, PIXE and EPBS results confirmed that ion-exchange also contributed to the adsorption process of uranium. All the results implied that the biosorption mechanism of uranium on Bacillus sp. is complicated and at least involves bioaccumulation, ion exchange and complexation process.

Adsorption behavior of U(VI) on doped polyaniline: the effects of carbonate and its complexes

Abstract In carbonate-buffer seawater or salt lake brines, three main uranium complexes, U(VI)-CO3 and Ca/Mg-U(VI)-CO3 complexes had been highlighted so far. In this paper, the effects of carbonate and its complexes on U(VI) adsorption onto doped polyaniline (PANI) were investigated using batch adsorption experiments. The adsorption equilibrium of U(VI) on doped PANI was reached within 30 min of contact time when U(VI)-CO3 complexes dominated the aqueous chemistry. Pseudo-second order and Langmuir isotherm models indicated that adsorption occurred on the homogeneous surface via monolayer chemisorption. Moreover, the increase in pHinitial, dissolved carbonate, calcium and magnesium concentrations could suppress the uranium adsorption process. The adsorption mechanisms under the weakly basic conditions were primarily involved in uranium anion species adsorption on nitrogen-containing functional groups instead of the anion exchange reactive sites on the doped PANI surface sites, whereas the U(VI)-CO3 complexes had a greater affinity than the Ca/Mg-U(VI)-CO3 complexes. The findings of this study are significant for the extraction of uranium resources from salt lake brines or seawater and for the prediction of uranium adsorption behaviors in weakly basic solution environments.